1. FIELD OF THE INVENTION
The present invention relates to a process of producing a novel hydrocarbon resin suitable as a tackifier for pressure-sensitive adhesives. The invention also relates to a pressure-sensitive adhesive containing the novel hydrocarbon resin produced by the process as a tackifier.
2. DESCRIPTION OF THE PRIOR ART
Pressure-sensitive adhesives are used for pressure-sensitive adhesive tapes or labels by coating the adhesives on base materials such as papers, cloths, and plastic films. Such pressure-sensitive adhesives must satisfy the following three criteria:
1. They must be tacky at normal temperature and have a high degree of tackiness.
2. They must have high adhesive strength.
3. They must have high breaking resistance, that is, high cohesion.
If adhesives are lacking in any one of the aforesaid three fundamental properties, they are not superior as adhesives. In general, as a base for pressure-sensitive adhesives, natural rubber or various synthetic rubbers are used but since such a rubber itself is insufficient in these fundamental properties, the insufficiency is supplemented by the addition of a tackifier. The tackifier also must have not only improved rubber-like properties but also excellent compatibility with rubber, high solubility in solvents, good color, high chemical stability, and excellent weatherability. A terpene resin has hitherto been used as the most excellent tackifier and other resins similar to a terpene resin, such as rosin, a derivative of rosin, a cumaroneindene resin, an aromatic petroleum resin, and an aliphatic petroleum resin have also been used for this purpose although they are inferior in properties to a terpene resin. However, since a terpene resin is prepared by polymerizing the .alpha.-pinene, .beta.-pinene, dipentene, etc., present in the volatile oils recovered from pine trees or oak trees, that is, is prepared using natural materials as a raw material, the supply of the resin is not stable and the cost of such a resin is not low.
Also, it may be possible to provide similar properties to the terpene resin to an aromatic petroleum resin by hydrogenating a part or all of the resin to an alicyclic structure but for this purpose the hydrogenation must be conducted under extreme conditions such as high temperature and high pressure and hence on considering these problems in the complicated nature of the steps and in the cost of the equipment, it has been difficult to obtain such a resin in a low cost.